(a) Field of the Invention
The present invention relates to a catalyst for a fuel cell, a method of preparing the same, a membrane-electrode assembly for a fuel cell including the same, and a fuel cell system including the same. More particularly, the present invention relates to a cathode catalyst having an improved catalytic activity and selectivity for reduction of an oxidant, and a membrane-electrode assembly including the same.
(b) Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and hydrogen in a hydrocarbon-based material such as methanol, ethanol, or natural gas.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell that uses methanol as a fuel.
The polymer electrolyte membrane fuel cell has an advantage of a high energy density and energy conversion efficiency, but it also has problems in the need to carefully handle hydrogen gas and the requirement of additional devices such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like in order to produce hydrogen as the fuel gas.
On the contrary, a direct oxidation fuel cell has a lower energy density than that of the polymer electrolyte membrane fuel cell, but it has the advantages of easy handling of a fuel, being capable of operating at room temperature, and no need for additional fuel reforming processors. Therefore, it has been acknowledged as an appropriate system for a portable power source for small electrical devices.
In the above fuel cells, the stack that generates electricity substantially includes several to scores of unit cells stacked in multiple layers, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly has an anode (also referred to as a “fuel electrode” or an “oxidation electrode”) and a cathode (also referred to as an “air electrode” or a “reduction electrode”) that are separated by a polymer electrolyte membrane.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.